How long does a commercial 6" carbon filter last?

Title kind of says it all.

a year....maybe year and a half max. I have used mine for a little while and need to get the carbon replaced. You will know when it starts to go bad.... It will stop covering up the smell

Ive always used home made versions, but after one grow the carbon shold be replaced.
But its cheep an availabel at most pet stores.

How big is your homemade filter and how much air do you push through it?

I say change the filter every year with the bulbs, don't be a cheap ass.

My big one is a bucket style one. 2x2 foot ish.